The present invention relates to welding devices such as a MIG welding machine, a TIG welding machine, an arc fusing type cutter, a fusing type cutter or an electric discharge machine in which a material is processed using an arc discharge, specifically, a machine of this type in which a high frequency electric source is employed to generate arcs contactlessly.
By way of example, a MIG welding machine will be described. In general, in a MIG welding machine, a wire-shaped electrode (hereinafter referred to as "a wire electrode" when applicable) is fused by the heat of electrical arcing or Joule heating into molten metal drops which are transferred onto a base material.
In a conventional MIG welding machine, the generation of an arc is carried out by bringing the wire electrode into contact with the base material momentarily to cause a shortcircuit current which heats and melts the wire electrode. The molten metal is scattered in the form of particles. The molten metal particles thus scattered may adhere to the surface of the base material. If this happens, it is necessary to remove the molten metal particles from the base material surface which operation decreases the overall work efficiency of the welding procedure.
This difficulty may be eliminated by utilizing with the MIG welding machine a contactless type arc generating mechanism using a high frequency electric source such as is employed in a TIG welding machine.
FIG. 1 shows the arrangement of a MIG welding machine so modified. In FIG. 1, reference numeral 1 designates a base material, 2 a torch, 3 a welding power source, 4a and 4b current supplying wires extending from the welding power source 3, and 5 a high frequency source composed of a series circuit including an oscillating coil 51, discharge gaps 52 and 53 and a high frequency oscillating capacitor 54. The high frequency source 5 oscillates, for instance, at 3 MHz when a high voltage is applied across terminals 55 by a high voltage source (not shown). A coupling coil 41 is formed by the current feeding wire 4 and it is coupled to the oscillating coil 51 so that, for instance, a high voltage of 5 KV is induced across the coupling coil 41. A high frequency bypass capacitor 6 is provided for the protection of the welding powder source 3. A wire electrode 8 (hereinafter referred to merely as "a wire 8" when applicable) is wound on a reel 7. A wire supplying unit 9 is made up of a driving motor 91, a drive roller 92 driven by the driving motor 91, and a wire depressing roller 93 adapted to press the wire 8 against the drive roller 92. The wire supplying unit 9 is controlled by a control device (not shown) to feed the wire 8 to the torch 2 at a rate corresponding to the particular welding conditions. In FIG. 1, reference character 8a designates the end portion of the wire electrode which protrudes from the torch 2. (The end portion will hereinafter be referred to as "electrode 8b" when applicable.) The wire 8 is inserted through a guide pipe (not shown), which is juxtaposed with the current feeding wire 4a, and into the torch 2 where electrical contact is made with the wire 8.
The operation of the MIG welding machine thus constructed will be described. In starting an initial arc, the high frequency electric source 5 is operated so that the output high frequency voltage of the high frequency electric source 5 causes a high frequency discharge between the electrode 8a and the base material 1. In response to the occurrence of the high frequency discharge, current is supplied from the welding power source 3 to generate and maintain an arc 10. The wire 8 from the reel is fed by the wire supplying unit 9. The electrode 8b is fused by the arc 10 thus generated and the base material 1 is welded along the welding line with the molten metal drops 8b formed from the electrode 8.
As was described above, a contactless type arc generating mechanism using a high frequency electric source, which is employed in a TIG welding machine, can be applied to a MIG welding machine. However, as the high frequency voltage is applied directly to the wire 8, it is necessary to electrically insulate the wire supplying unit 9 and the reel 7, that is, to provide a high frequency insulation treatment for these members so that they can sufficiently withstand the high voltage of high frequency.